In gas turbine engines air usually is compressed at an initial stage, then is heated in combustion chambers, and the hot gas so produced drives a turbine that does work, including rotating the compressor.
To achieve a good overall efficiency in a gas turbine engine, one consideration is the reduction of losses of air pressure, such as due to friction and turbulence, between the air compressor and the intakes of the combustion chambers. In a common gas turbine engine design, compressed air flows from the air compressor, through a diffuser, into a plenum in which are positioned transitions and other components, and then from the plenum into the intakes of combustion chambers.
One general approach to improve airflow efficiency in the plenum, and thereby improve overall efficiency, is to modify the end of the diffuser so as to redirect air more radially outward. For example, a curved diffuser may be employed wherein the outlet end has a bend that directs the airflow radially outward, instead of axially aft. Conceptually this may provide 1) a more direct, flow-efficient route to the combustion chamber intakes, and 2) less travel and turbulence/losses in the parts of the plenum where the mid-sections and aft ends of the transitions are located.
However, radial diversion of a substantial portion of compressed air, without more, may present a problem when the airflow from the compressor has been used, or is desired to be used, to cool the transitions. Generally, transition cooling may be effectuated fully or partially by any of the following, which represents a non-exclusive list: closed circuit steam cooling (i.e., see for one example U.S. Pat. No. 5,906,093); open air cooling (in which a portion of the compressed air passes through channels in the transition and then enters the flow of combusted gases within the transition, see for one example U.S. Pat. No. 3,652,181); convection cooling (see for one example U.S. Pat. No. 4,903,477); effusion cooling (i.e., conveying air from outside the transition through angled holes into the transition); channel cooling (i.e., conveying air from outside the transition, through channels in the transition walls, and into the transition); and impingement cooling (where air is directed at the transition exterior walls through apertures positioned on plates or other structures close to these walls, see U.S. Pat. No. 4,719,748 for one example). It also is noted that some of these approaches may be used in combination with one another.
Notwithstanding the features of current cooling approaches, when compressor air is desired to cool the transition, and when a more efficient design, such as a curved diffuser, is desired for airflow, there is a need for an appropriately designed combination of airflow-directing elements to attain a reliable, desired balancing of overall airflow efficiency and of transition cooling. As disclosed in the following sections, the present invention provides airflow-directing assemblages that are effective to achieve this desired balance. That is, the present invention advances the art by solving the dual, potentially conflicting issues of cooling of transitions and conservation of airflow and pressure to the combustion chambers.